Methods for varying the pile height or pile lengths while weaving terry fabric and looms for performing such methods are known in the art. These methods and devices employ the principle of so-called fabric shifting. The following publications describe this principle, European Patent Publication EP 0,518,809 A1; Japanese Patent Publication JP 07-145534; U.S. Pat. No. 5,518,037 and European Patent Publication 0,768,407 A1. Looms equipped with conventional devices for the varying of the pile height or length as described in the above references include pile height adjustment mechanisms which are controllable independently of the main drive of the loom. Such devices require a substantial effort and expense for their construction and for accomplishing their function.
A known terry fabric weaving loom has a rotatably supported fabric take up roller with a reed which performs in a repetitive motion rhythm weft thread partial beat-ups and a weft thread full beat-up. A number of partial beat-ups and at least one full beat-up form a group of beat-ups. The pile height formation mechanism includes a motion transmission coupling, the drive of which is derived from the main loom drive and may be blocked. The drive connection to the main loom drive is accomplished by an eccentric cam drive. Coupling elements transmit the drive of the eccentric cam to the fabric take-up roller for shifting the actual beat-up line of the fabric relative to a base beat-up line in the loom. Such a machine is capable of forming either a smooth fabric or a fabric with one pile height. Varying the pile height or length is not possible.